Fail-safe proportional mixing valve

ABSTRACT

A fail-safe proportional mixing valve is provided that tempers a hot fluid supply by proportional flow from a hot fluid inlet and a cold fluid inlet. The valve includes a fail-safe mechanism disposed within the body of the valve to isolate flow from the hot fluid inlet in the event the temperature of the mixed fluid exceeds a predetermined set point. The valve also includes a check valve in the fluid inlets to prevent backflow in case of failure of a fluid supply. In a further aspect, the cold fluid inlet includes an adjustment set screw to adjust the cold fluid flow into the mixing valve, thereby adjusting the maximum mixed fluid temperature that can be discharged from the valve assembly.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a proportional mixing valve for mixinga hot and a cold fluid that includes a fail-safe mechanism for shuttingoff hot fluid flow when the temperature of the fluid exiting the valveexceeds a predetermined set point.

[0002] Mixing valves and fail-safe mechanisms in water and other fluidsupply systems are well known. They are typically employed to controlthe maximum fluid temperature to a predetermined set point, which isusually a temperature, that is safe for human skin upon prolongedexposure. For example, hot water from water heaters typically has atemperature of 140° F. to 160° F. with a maximum temperature of 180° F.At 140° F., a child can be scalded if the skin is exposed for onesecond. However, if the water temperature is reduced to 120° F.continuous exposure for five minutes is required to scald the skin.

[0003] In domestic applications, and in many commercial uses, it isdesirous that the maximum hot water temperature from a shower, tub orbasin outlets be set at a level that prevents serious burning orscalding of the skin. Oftentimes, a water faucet is allowed to run in afull flow hot water condition to purge cold water resting in the supplyline to the faucet. A child or other unsuspecting person would bescalded if they were to contact the water once the cold water is purged.Thus, mixing valves are often used in the supply piping to basin, tub,or shower faucets in order to temper the hot water supply. Tempering thehot water supply at these point-of-use locations allows highertemperature water to continue to be produced by a water heater and usedat locations where it is necessary, such as the washing machine ordishwasher.

[0004] While mixing valves temper the hot water supply under normaloperating conditions, a fail-safe mechanism is necessary to isolate theflow of hot water when the supply of cold water fails. Serious injurycould result to a child if, for instance, the cold water supply failswhile the child is taking a shower, causing the water temperature toincrease to its maximum supply temperature. Thus, fail-safe mechanismscan provide an added protective feature when combined with a mixingvalve that is used to temper hot water.

[0005] Previous patents of mixing valves and fail-safe devices for hotfluid have employed various techniques. For example, U.S. Pat. No.4,299,354 to Ketley discloses a thermally operated mixing valve. Thetemperature of the fluid is controlled via a thermally responsivecontrol member that varies the flow of the cold fluid as needed totemper the hot water to the desired preset temperature. If the coldwater supply fails or is interrupted, the control member reacts toeither restrict or nearly isolate hot water flow. The valve is typicallylocated at the point-of-use of the fluid supply since the user mustmanually operate the control member with an actuator to obtain fluid ata temperature less than the preset maximum temperature.

[0006] Another type of device is disclosed in U.S. Pat. No. 4,480,784 toBennett and U.S. Pat. No. 3,938,741 to Allison. Each of these patentsdiscloses safety devices for isolating water flow to an outlet when thewater temperature exceeds a predetermined set point. Both devices areemployed in the apparatus, which discharges the water, such as ashowerhead. The Bennett devices employs a thermostatic cup that expandsto constrict flow, but allows the hot water to drip so that the devicecontinues sensing the water temperature. The Allison device includes atemperature responsive mechanism with a valve attached to one end thatisolates flow when the water temperature exceeds a given operatingtemperature.

[0007] The foregoing prior art suffers from several drawbacks. Forinstance, the mixing valve device must be located near where the flow offluid is controlled by the user. The devices also rely on a modulatingcontrol member to temper the hot water supply whose setting iscontrolled by the user's manipulation of an actuator. In some valves,the fail-safe devices are required to be on or near a water supplysystem is required to temper the hot water supply temperature.

[0008] Another desirable feature absent from these prior systems is theability to adjust the fluid temperature at the point-of-use outlet.Different maximum temperatures may be desirable at different dischargeoutlets, such as a kitchen sink versus a workroom tub.

[0009] What is needed, therefore, is a mixing valve assembly, which doesnot require modulating elements in order to temper the hot fluid supply.What is also needed is a mixing valve assembly, which includes afail-safe mechanism that allows the valve to be used in virtually anylocation in a domestic or commercial water supply or fluid supplysystem.

SUMMARY OF THE INVENTION

[0010] A proportional flow mixing valve assembly is provided that allowsa hot fluid supply to be tempered with a predetermined proportional flowof cold fluid based on the relative inlet diameters of the hot and coldfluid supplies. The assembly also includes a fail-safe mechanism, whichisolates the hot fluid flow in case of interruption of the cold fluidsupply. The assembly may also be provided with a check valve to preventbackflow of the hot fluid supply into the cold fluid supply in the eventof its failure or interruption.

[0011] In particular, the assembly can mix a hot fluid with a cold fluidto achieve a mixed fluid that has a temperature below a specifiedthreshold. The fluids are proportionately mixed in a mixing chamber inorder to temper the hot fluid temperature. The desired temperature isobtained based on the sizing of relative inlet diameters allowingproportional flow from the hot and cold fluid inlets. When the coldfluid supply is interrupted or fails, a failure responsive meansisolates the hot fluid flow when the mixed fluid temperature in themixing chamber exceeds a predetermined set point temperature. The setpoint temperature is typically set such that the mixed fluid temperaturewill be safe with prolonged exposure to the human skin.

[0012] The failure response means includes a fail-safe mechanism, whichis biased in an open position. The fail-safe mechanism can include ahousing containing a thermally responsive medium, which volumetricallyreacts to changes in the fluid temperature in the mixing chamber. Thethermally responsive medium is engaged to a plug, which moves toward thehot fluid inlet as the fluid temperature increases. When the fluidtemperature exceeds a predetermined threshold, the plug isolates the hotfluid supply. The valve assembly may also include a check valve in thecold fluid inlet to prevent backflow or siphoning upon failure orinterruption of the hot fluid supply.

[0013] In a further embodiment, a flow control member is interposed atone of the fluid inlets, such as the cold inlet. The flow control memberis adjustable to permit adjustment of the limit temperature of the mixedfluid discharged from the valve. the adjustable flow control member caninclude a stepped diameter screw that is advanced across the inlet fluidflow to reduce the flow in relation to the stepped diameter. Thisadjustable flow control member does not interfere with the fail-safefunctioning of the valve, but instead allows the user to specificallydetermine the maximum mixed fluid temperature at a particular fixture orfaucet.

[0014] One object of the present invention is to provide a mixing valvein which the relative diameters of the fluid inlets are proportionatelysized to control the mixed fluid temperature below a safe thresholdtemperature. Another object of the present invention is to provide afail-safe assembly that isolates hot fluid flow then the mixed fluidtemperature exceeds the threshold level due to, for instance, failure ofthe cold fluid supply.

[0015] It is yet another object of the present invention to provide afail-safe proportional mixing valve with a means for preventing backflowinto a failed or low pressure fluid supply line from the intact supplyline. A further object is accomplished by features that permitadjustment of the maximum mixed fluid temperature discharged from themixing valve assembly, without sacrificing the fail-safe features of theassembly.

[0016] These and other objects of the present invention will become moreapparent from the following description of the preferred embodiment andthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view of one embodiment of a fail-safeproportional mixing valve in accordance with the present invention.

[0018]FIG. 2 is an exploded side elevational view of theproportional-mixing valve of FIG. 1.

[0019]FIG. 3 is an exploded view of a portion of the fail-safe mechanismillustrated in FIG. 2.

[0020]FIG. 4 is a section view of the proportional mixing valve of FIG.1 illustrating the fail-safe mechanism in a closed position.

[0021]FIG. 5 is a section view of the proportional mixing valve of FIG.1 illustrating the fail-safe mechanism in a closed position.

[0022]FIG. 6 is a perspective view of the valve employed in the fluidinlets as shown in FIGS. 4 and 5.

[0023]FIG. 7 is an isometric view of a piping system illustrating oneexample of use of the proportional mixing valve of FIG. 1

[0024]FIG. 8 is a side elevational view of a fail-safe mixing valvesimilar to the valve in FIGS. 1-6 with the additional ability to controlthe maximum mixed outlet temperature for the valve.

[0025]FIG. 9 is a side cross-sectional view of the mixing valve shown inFIG. 8.

[0026]FIG. 10 is an enlarged partial cross-sectional view of the mixingvalve of FIGS. 8-9 with the flow control member in a first position.

[0027]FIG. 11 is an enlarged partial cross-sectional view of the mixingvalve of FIGS. 8-9 with the flow control member in a first position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] For the purpose of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0029] In accordance with the present invention, a device forproportionally mixing hot and cold fluid, which includes a fail-safemechanism, is shown in FIGS. 1-7. Referring to FIG. 1, the mixing valve10 includes a cold fluid inlet 11 for supplying a cold fluid, a hotfluid inlet 12 for supplying a hot fluid, and a mixed fluid outlet 13for discharging a tempered fluid. Inlets 11 and 12 are connected tovalve body 14. Valve body 14 defines a cavity 23 (FIG. 2) which servesas mixing chamber. The inlets 11 and 12 communicate with cavity 23 inorder for the hot and cold fluids to mix in cavity 23, creating thetempered fluid. Mixed fluid outlet 13 is also in communication withcavity 23 and allows the tempered fluid to exit cavity 23.

[0030] Referring now to FIG. 2, cold fluid inlet 11 and hot fluid inlet12 are sized to allow proportional flow of hot and cold fluid to temperthe water in cavity 23 before it exits through mixed fluid outlet 13. Ina preferred embodiment, the mixed fluid has a temperature of about 120°F., which will prevent scalding of the skin upon short-term exposure(less than 5 minutes). Alternative embodiments contemplate other outletfluid temperatures depending on the intended use of the mixed fluid. Insome configurations, the outlet temperature can be controlled to a smalldegree by adjusting the cold water flow through inlet 11. In theseconfigurations, a needle valve can be connected at the cold inlet 11 tocontrol the cold flow into the valve body 14.

[0031] One specific embodiment of the mixing valve assembly will now bedescribed. In one typical domestic use, outlet 13 is sized to allow aflow of three gallons of water per minute. Typically, the cold fluidsupply is about 55° F., and the hot water supply temperature fromdomestic water is about 140° F. The hot and cold fluid inlets are sizedto allow a flow of hot water and a flow of cold water that will temperthe mixed water to about 120° F. In the specific embodiment, hot fluidinlet 12 has a diameter of 0.23 inches, and cold fluid inlet 11 has adiameter of 0.13 inches. The ratio of hot fluid flow to cold fluid flowis about 3.1 to 1, resulting in a mixed fluid temperature of less than120° F.

[0032] Cavity 23 defines a longitudinal axis 24, which extends throughthe center of hot fluid inlet 11. Fail-safe mechanism 30 is positionedwithin cavity 23 and centered along longitudinal axis 24. Mixing device10 includes a first spring 31 and centered along longitudinal axis 24.Mixing device 10 includes a first spring 31 and a second spring 36disposed within cavity 23. Springs 31 and 36 bias fail-safe mechanism 30to an open position, as shown in FIG. 4. First spring 31 contacts amixing chamber bearing surface 20 and a plug flange 40. Second spring 36contacts an outlet bearing surface 21 and a thermostat-housing flange45. When mixing outlet 13 is threaded or attached to valve body 14,first spring 31 and second spring 36 compress and the opposing forcefrom each spring ensures that fail-safe mechanism 30 is aligned alonglongitudinal axis 24 within cavity 23. A washer 39 may also be includedto maintain the positioning of fail-safe mechanism 30 along longitudinalaxis 24. Washer 39 includes prongs 46 spaced about its circumference,which project outward to bear on the side walls of cavity 23. Prongs 46also allow fluid flow around washer 39.

[0033] Referring back to FIG. 2, fail-safe mechanism 30 includes a plug32, a piston 33 which includes a first end and a second end, a sleeve 34and a thermostat housing 35. Plug 32 defines a recess 41, which engagesone end of piston 33. The opposite end of piston 33 is positioned withinsleeve 34. As shown in FIG. 3, sleeve 34 includes sleeve flanges 42 fitwithin recess 43. Thermostat cavity 37 includes an amount of thermalexpansion material 37. In one embodiment, the thermal expansion material37 includes a thermally responsive wax, which volumetrically changeswith changes in temperature. In another embodiment, the thermalexpansion material 37 includes a memory metal, which expands andcontracts with temperature changes. In any event, the end of piston 33disposed within sleeve 34 is in contact with the thermal expansionmaterial disposed within thermostat cavity 37.

[0034] Valve body 14 includes mixing chamber threads 15, whichthreadedly engage first outlet threads 16. Fail-safe mechanism 30 andsprings 31 and 36 are positioned with cavity 23 prior to assembly ofoutlet 13. Outlet 13 is threaded onto valve body 14, compressing springs31 and 36 as it is threaded into place. Springs 31 and 36 are sized sothey are neither fully compressed nor fully relaxed when the mixingdevice 10 is assembled, thus allowing fail-safe mechanism 30 to expandand contract. An O-ring gasket 38 is provided to seal mixed outlet 13and valve body 14 when assembled.

[0035] Referring now to FIG. 5, plug 31 prevents flow from hot fluidinlet 12 when the mixed fluid temperature in cavity 23 exceeds apre-determined threshold temperature. As the temperature of the mixedfluid increases, thermal expansion material 37 in thermostat housing 35expands in sleeve 34. This expansion causes piston 33 move plug 32towards hot fluid inlet 12, lengthening fail-safe mechanism 30 andfurther compressing first spring 31 and second spring 36. When thetemperature of the fluid exceeds the set point temperature, plug 32engages hot fluid inlet 12 and prevents further flow of hot fluid.

[0036] Valve body 14, inlets 11 and 12 and outlet 13 are preferablymolded from a cast gunmetal and cavity 23 is machined to the requireddimensions as is known in the art. The components of the fail-safemechanism 30 are preferably made of brass to prevent rust and corrosionfrom affecting their performance. Springs 31 and 36 are preferably madeof stainless steel. However, other materials know in the art, which canwithstand the temperature differentials, and meet the performancerequirements described above are also contemplated.

[0037] Hot and cold fluid inlets 11 and 12 may include inlet threads 18,and mixed outlet 13 may include second outlet threads 17. These threadsmay be threadedly engaged to compression couplings 22, which are used toconnect mixing valve 10 to a fluid supply system as is known in the art.Alternatively, flared ends or beveled ends may replace the threads andcouplings on the inlets and outlet so the valve may be welded orsoldered onto adjacent piping of the water supply system.

[0038] Check valves 50, as shown in FIGS. 4 and 5, may be installed ineach fluid inlet 11 and 12 to prevent backflow in event of a hot or coldfluid supply disruption. Referring now to FIG. 6, check valve 50includes a cylindrical body 51, a first opening 52 on one end defined bycylindrical body 51, and flaps 54 extending from the opposite end ofcylindrical body 51. Flaps 54 are connected along the two opposite edgesextending from body 51 in order to define a second opening 53. Whenfluid is flowing through first opening 52, flaps 54 are forced apart bythe fluid pressure to enlarge second opening 53. When there is no fluidflow through first opening 52, flaps 54 some together and prevent anyfluid from the opposite direction from flowing into second opening 53,thus preventing backflow from the hot water supply into the cold watersupply.

[0039]FIG. 7 illustrates the use of the preferred embodiment-mixingvalve 10 in a typical domestic water supply system. Shower 60 isconnected to a cold water system 64 and a hot water system 65. Hot watersystem 65 is connected to a water heater 66, which heats water suppliedfrom a well or water system to about 140-180° F. At this temperature,the hot water would cause a full depth scald of a child's skin in onesecond. Mixing valve 10 is placed in the hot water system with hot fluidinlet 12 receiving water from water heater 66. Cold fluid inlet 11 isconnected to cold water system 64. The hot water and cold water mix invalve body 14. The cold water inlet 11 is sized such that the cold watertempers the hot water, preferably to a temperature of about 120° F. Atthis temperature, a child's skin would have to be in contact with thewater for about five minutes to be scalded. The tempered water exits themixing valve 10 through mixed fluid outlet 13. The tempered water fromhot can again be proportioned by user control of a hot water valve 61and a cold water valve 62 to mix at a junction 63 prior to exiting atshower 60.

[0040] Oftentimes before using a shower or tub, it is necessary to purgecold water from a water supply system. Opening hot water valve 61 whilecold water valve 62 remains closed does this. Once the cold water ispurged, only water from hot water supply 65 is coming out of shower 60.If the hot water temperature were not tempered, its temperature exitingfrom shower 60 would be 140-180° F. A person or child touching the watercould be seriously burned if cold water supply 64 was inadvertently notopened. The device 10 tempers the hot water supply 65 to a safetemperature of below 120° F. by allowing a continuous mixing of coldwater supply 64 in valve body 14, even though only hot water valve 61opened by the user.

[0041] Another advantage of the present invention is recognized uponfailure of cold water supply 64. The fail-safe mechanism 30, shown inFIG. 5, will prevent flow from the hot water supply line 65 when thetemperature of the water in valve body 14 exceeds a predeterminedthreshold temperature. Preferably, this threshold is about 120° F. Ifcold water supply 64 were to fail due to, for instance, a main burst,then the water from water heater 66. Fail-safe mechanism 30 will thenreact to isolate hot water supply 64 from shower 60. An alternativeembodiment may also include check valve 50 in cold fluid inlet 11. Thisprevents backflow from hot water system 65 into cold water system 64 andthe possibility of injury occurring to a person using cold water system64.

[0042] A further embodiment of the invention is depicted in FIGS. 8-11.In this embodiment, a mixing valve assembly 70 is configured similar tothe valve assembly 10 previously described. The valve assembly 70includes a hot inlet 12 and a mixed fluid outlet 13. A valve body 14includes a cavity 23 within which hot fluid from inlet 12 and cold fluidare mixed. In this embodiment, cold fluid is supplied through cold inlet71, which is modified relative to the cold inlet 11 of the embodiment ofFIG. 1. Specifically, the cold inlet 71 includes an enlarged portion 73that is preferably configured to include an external hex for engagementwith a driving wrench. The wrench can be used to thread the cold inlet71 into the valve body 14 as described above for cold inlet 11.

[0043] The cold inlet 71 defines a cold inlet bore 75 that communicateswith the mixing chamber cavity 23 when the cold inlet is engaged to thevalve body 14. As shown most clearly in FIG. 9, the cold inlet bore 75has a reduced diameter portion 76 within which the check valve 50resides. The cold inlet bore 75 steps down to a further reduced diameterportion 78 that preferably continues to the engagement end 79 of thecold inlet 71.

[0044] In a further feature of the mixing valve assembly 70, theenlarged portion 73 defines a blind adjustment bore 80 extendingtransversely to and intersecting the cold inlet bore 75. The adjustmentbore 80 includes a threaded portion 82 at its blind end and anintermediate reduced diameter segment 84 at the intersection with thecold inlet bore 75. A flow control member 90 extends into the adjustmentbore 80. In the preferred embodiment, the flow control member is anadjustment screw 90 that has a threaded end 92 for engagement with thethreaded portion 82 of the adjustment bore 80. The adjustment screw 90also includes an enlarged driving head 94 at its opposite end that isconfigured to receive a driving tool, such as a screwdriver. The drivinghead 94 has a diameter slightly smaller than the diameter of theadjustment bore 80 at its open end, but larger than the diameter of theintermediate segment 84.

[0045] Further details of the adjustment screw 90 can be discerned fromFIGS. 10-11. The adjustment screw includes an elongated shaft portion 96that has an outer diameter less than the intermediate portion 84 of theadjustment bore 80 so that the adjustment screw 90 can move axiallyalong the bore 80 and particularly intermediate portion 84. This axialmovement is accomplished by threading the adjustment screw 90 into andout of the threaded portion 82 of the adjustment bore 80. Preferably,the valve assembly 70 includes a seal 97 between the shaft 96 and theadjustment bore portion 84 to prevent fluid leakage through theadjustment bore 80.

[0046] The adjustment screw 90 includes an increased diameter land 98intermediate along the length of the shaft portion 96. The land 98 has adiameter slightly smaller than the diameter of the intermediate portion84 of the adjustment bore 80. The width of the land 98 is calibrated tobe slightly less than the diameter of the reduced diameter portion 78 ofthe cold inlet bore 75.

[0047] The adjustment screw 90 can be adjusted between the two positionsshown in FIG. 10 and FIG. 11. In the first position, the land 98 iscompletely interposed within the cold fluid inlet bore and particularlythe reduced diameter portion 78. When the land 98 is so positioned, thecold fluid flow is substantially interrupted. Depending upon the widthof the land relative to the diameter of the portion 78, the cold flowcan be reduced to a trickle, although preferably the components aresized so that a 3 g.p.m. cold fluid flow rate is reduced to 1 g.p.m.

[0048] In the second position shown in FIG. 11, the land 98 issubstantially moved out of the cold inlet bore flow path so the standardcold flow is maintained. It is contemplated that the length of theadjustment screw 90 can be determined with respect to the length of theadjustment bore 80 so that the overall stroke of the intermediate land98 can be calibrated. Moreover, the land 98 itself can have variousconfigurations to control the fluid flow around or even through the land98. For example, the land 98 or shaft 96 can have different diameterportions to provide incremental flow control. In other words, thereduction in flow through one of the inlets is in proportion to thediameter of the portion of the land 98 or shaft 96 that intersects thefluid flow. These design modifications still retain the primary functionof the adjustment screw 90 of providing means for adjusting the limitingtemperature of the mixing valve 70. As discussed in connection with theprevious mixing valve assembly 10, the mixing valve receives hot andcold water at relatively constant temperatures. The fail-safe componentsof the valve are calibrated to a particular temperature at which hotflow is reduced to a trickle upon failure of the cold fluid inlet. Thefail-safe components do not provide any means within the valve assemblyfor adjusting the maximum mixed fluid temperature discharged from thevalve assembly.

[0049] The adjustment screw 90 and the cold fluid inlet 71 of thepresent embodiment permit adjustment of the cold fluid flow into themixing chamber 23, and therefor adjustment of the maximum mixedtemperature that the valve assembly 70 can achieve. While in theillustrated embodiment the flow control member/adjustment screw isdisposed only within the cold fluid inlet, the flow control member canbe utilized within the hot fluid inlet, either alone or in conjunctionwith a similar member in the cold fluid inlet. The flow control member90 can be utilized in the inlet having the higher input flow rate, whichis typically the cold fluid inlet, to help balance the hot/cold flowrates.

[0050] This adjustment feature greatly enhances the utility of themixing valve of the present invention. Specifically, certain householdfaucets may have different water temperature needs. For example, thetemperature requirements for a shower may differ from at the kitchensink, which may differ from the requirements at a workroom basin. Somehousehold usages may require water that has a lower limitingtemperature, such as a child's bathroom sink, to prevent scalding of achild washing his/her hands. On the other hand, a kitchen sink mayrequire a higher limiting temperature for hand washing of dishes. Theadjustment features of the mixing valve 70 address these variabletemperature requirements in a single valve without compromising thefail-safe features of the valve. Separate mixing valves 70 can be placedat different locations throughout the house, each valve beingindividually adjusted so that the maximum water discharge temperaturecan be matched with the usage at that location.

[0051] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiments have been shown and described andthat all changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A fail-safe proportional mixing valve assembly,comprising: a valve body defining a mixing chamber; a cold fluid inletin communication with said mixing chamber and connected to a supply of afirst flow of a cold fluid; a hot fluid inlet in communication with saidmixing chamber and connected to a supply of a second flow of a hotfluid; a fluid outlet in communication with said mixing chamber fordischarge of fluid therefrom, wherein said cold fluid inlet and said hotfluid inlet are proportionately sized to temper the hot fluid withinsaid mixing chamber below a predetermined set point temperature; andfailure responsive means for substantially restricting said second flowof hot fluid into said mixing chamber upon a failure of said first flowof cold fluid, said failure responsive means being at least partiallydisposed within said mixing chamber and including; a thermal expansionmember disposed in said mixing chamber that volumetrically changes inproportion to the fluid temperature in the mixing chamber; a plugdisposed between said hot fluid inlet and said mixing chamber andengaged to said thermal expansion member to move with said member froman open position which allows substantially full flow from said hotfluid inlet, to a closed position in which said plug substantiallyrestricts flow from said hot fluid inlet; and biasing means for biasingsaid plug to said open position when the temperature of fluid withinsaid mixing chamber is below said set point.
 2. The mixing assemblyaccording to claim 1, further comprising a check valve position withinsaid cold fluid inlet to prevent backflow of hot fluid from said mixingchamber into said cold fluid inlet upon interruption of the first flowof cold fluid.
 3. The mixing assembly according to claim 1, wherein saidfailure responsive means includes a cylindrical housing defining ahollow interior, with said thermal expansion member being disposedwithin said housing in communication with said hollow interior.
 4. Themixing assembly according to claim 1, wherein said thermal expansionmember includes a thermal responsive wax.
 5. The mixing valve assemblyaccording to claim 1, wherein said biasing means includes a first springdisposed between said hot fluid inlet and said plug to bias said plugaway from said hot fluid inlet.
 6. The mixing valve assembly accordingto clam 5, wherein said biasing means includes a second spring operatingon said plug and opposing said first spring, wherein said first springand said second spring are arranged to support said plug within saidhollow interior of said mixing chamber and to maintain alignment of saidplug with said hot fluid inlet.
 7. The mixing valve assembly accordingto claim 1, wherein said cold fluid inlet defines a cold inlet bore witha first diameter and said hot fluid inlet defines a hot inlet bore witha second diameter greater than said first diameter.
 8. The mixing valveassembly according to claim 7, wherein said second diameter is more than1.5 times greater than said first diameter.
 9. The mixing valve assemblyaccording to claim 8, wherein said first diameter is about 0.13 inchesand said second diameter is about 0.23 inches.
 10. A fail-safe mixingvalve assembly, comprising: a valve body defining a mixing chamber; acold fluid inlet in communication with said mixing chamber and connectedto a supply of a first flow of a cold fluid; a hot fluid inlet incommunication with said mixing chamber and connected to a supply of afirst flow of a hot fluid; failure responsive means for substantiallyrestricting said second flow of hot fluid into said mixing chamber upona failure of said first flow of cold fluid, said failure responsivemeans being at least partially disposed within said mixing chamber; anda flow control member disposed within at least one inlet of said coldfluid inlet or said hot fluid inlet, said flow control member includingan adjustment screw having a stepped diameter shaft, said adjustmentscrew being adjustably disposed within said one inlet to introduceportions of said stepped diameter shaft into the corresponding firstflow or second flow through said one inlet to reduce said correspondingflow in proportion to the diameter of said portions of said shaft. 11.The fail-safe mixing valve assembly according to claim 10, wherein saidone inlet includes: an inlet bore in communication with said mixingchamber; an enlarged portion defining an adjustment bore therethroughintersecting said inlet bore, said adjustment bore having a threadedportion for threaded engagement with said adjustment screw.
 12. Thefail-safe mixing valve assembly according to claim 11, wherein: saidinlet bore has a diameter at the intersection with said adjustment bore;and said stepped diameter shaft of said adjustment screw includes anadjustment land having a dimension along the length of said shaft thatis slightly less than said diameter of said inlet bore.
 13. Thefail-safe mixing valve assembly according to claim 12, wherein: saidadjustment bore has an adjustment diameter at the intersection with saidinlet bore; and said adjustment land has an outer diameter that isslightly less than said adjustment diameter of said adjustment bore. 14.The fail-safe mixing valve assembly according to claim 13, wherein saidthreaded portion of said adjustment bore is configured to permitthreaded adjustment of the adjustment screw within the adjustment borefrom a first position in which said adjustment land is entirely disposedwithin said diameter of said inlet bore at the intersection, and asecond position in which said adjustment land is disposed substantiallyoutside said diameter of said inlet bore at the intersection.